There has been tremendous focus in the polyolefin industry on developing new and improved metallocene catalyst systems, designing catalyst systems to produce new polymers, to improve operability or processability of catalyst systems, and to improve catalyst productivity. Reactor conditions and the catalyst employed in the polymerization can affect numerous physical and chemical properties of the polymer, including molecular weight, molecular weight distribution, compositional distribution, crystallinity and melting temperature, and extractable content (e.g. hexane extractables), among others. Reactor conditions and the catalyst employed in the polymerization can also affect the processability of the resulting polymer. Polymer processability refers to the ability to economically process and shape a polymer uniformly. Processability involves such elements as how easily the polymer flows, melt strength, and whether the extrudate is distortion free. Small changes in mechanical properties and polymer processing flexibility are welcomed by end users.
In addition to the several reactor and reactant process control variables which may be manipulated during production, polymer product properties may also vary based upon catalyst formulation and structure. The metal atom and the ligands (pi-bonded moieties) forming the metallocene complex can affect the properties of the polymer product formed. The support architecture, the number of functional groups on the support (such as —OH groups on silica), the activator loading, and the pre-impregnated catalyst loading can also affect the product formed.
Recent advances in polymerization and catalysis have resulted in the ability to produce many new polymers having improved physical and chemical properties useful in a wide variety of superior products and applications. Regardless of these technological advances in the polyolefin industry, common problems, as well as new challenges still exist. There is a need, therefore, for improved catalysts that have improved activity and produce polymer products that have improved properties. Applicants have now found that catalyst performance and properties of the polymer product formed may be influenced by the manner in which the catalyst is delivered to a gas phase polymerization system.